U.S. patent application number 12/731048 was filed with the patent office on 2010-08-05 for distance measuring instrument and method.
This patent application is currently assigned to Trimble 3D Scanning. Invention is credited to Auguste D'Aligny, Richard Day, Yuri P. Gusev.
Application Number | 20100195088 12/731048 |
Document ID | / |
Family ID | 39434328 |
Filed Date | 2010-08-05 |
United States Patent
Application |
20100195088 |
Kind Code |
A1 |
D'Aligny; Auguste ; et
al. |
August 5, 2010 |
DISTANCE MEASURING INSTRUMENT AND METHOD
Abstract
A distance measuring instrument comprises at least one light
source; at least one light detector; optics to direct measuring
light emitted from the at least one light source towards an object
and to direct measuring light received back from the object to the
at least one detector; a signal delay module; a first signal
analyzer; and a variable gain amplifier.
Inventors: |
D'Aligny; Auguste; (Paris,
FR) ; Day; Richard; (Fontenay-Sous-Bois, FR) ;
Gusev; Yuri P.; (Alvsjo, SE) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Trimble 3D Scanning
Fontenany-Sous-Bois
FR
|
Family ID: |
39434328 |
Appl. No.: |
12/731048 |
Filed: |
March 24, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP2007/008487 |
Sep 28, 2007 |
|
|
|
12731048 |
|
|
|
|
Current U.S.
Class: |
356/5.01 |
Current CPC
Class: |
G01S 7/4868 20130101;
H03G 3/3084 20130101; G01C 3/08 20130101; G01S 7/497 20130101; G01S
7/4814 20130101; G01S 7/4818 20130101; G01S 17/10 20130101 |
Class at
Publication: |
356/5.01 |
International
Class: |
G01C 3/08 20060101
G01C003/08 |
Claims
1. A distance measuring instrument comprising: at least one light
source; at least one light detector; optics to direct measuring
light emitted from the at least one light source towards an object
and to direct measuring light received back from the object to the
at least one detector; a signal delay module; a first signal
analyzer; and a variable gain amplifier; wherein: an output of the
at least one light sensor is connected to an input of the signal
delay module; the output of the at least one light sensor is
connected to a signal input of the first signal analyzer; an output
of the signal delay module is connected to a signal input of the
variable gain amplifier; and an output of the first signal analyzer
is connected to a gain setting input of the variable gain
amplifier.
2. The distance measuring instrument according to claim 1 wherein a
signal delay time provided by the signal delay module is greater
than a processing time associated with the first signal
analyzer.
3. The distance measuring instrument according to claim 1 wherein a
signal delay time provided by the signal delay module is greater
than a settling time associated with the variable gain
amplifier.
4. The distance measuring instrument according to claim 1 wherein a
signal delay time provided by the signal delay module is greater
than 0.5 ns.
5. The distance measuring instrument according to claim 1 wherein
the signal delay module comprises a surface acoustic wave
device.
6. The distance measuring instrument according to claim 1 wherein
the first signal analyzer is configured to provide an output signal
at its output which is indicative of a peak value of an input
signal supplied to its signal input.
7. The distance measuring instrument according to claim 1 wherein
the first signal analyzer comprises an amplitude detector.
8. The distance measuring instrument according to claim 1 wherein
the first signal analyzer comprises a reset input.
9. The distance measuring instrument according to claim 1 wherein
the variable gain amplifier comprises a divider circuit.
10. The distance measuring instrument according to claim 9 wherein
the divider circuit comprises an operational amplifier and a
multiplier circuit.
11. The distance measuring instrument according to claim 1 wherein
the variable gain amplifier comprises a divider circuit and a first
multiplier circuit, wherein an output of the divider circuit is
connected to a first input of the first multiplier circuit.
12. The distance measuring instrument according to claim 11 wherein
a first input of the divider circuit is connected to the output of
the first signal analyzer, and a second input of the first
multiplier is connected to the output of the signal delay
module.
13. The distance measuring instrument according to claim 11 wherein
the variable gain amplifier further comprises a second multiplier,
wherein a first input of the second multiplier is connected to the
output of the signal delay module, an output of the second
multiplier is connected to a second input of the first
multiplier.
14. The distance measuring instrument according to claim 13 wherein
the variable gain amplifier further comprises a square rooter,
wherein an input of the square rooter is connected to an output of
the first signal analyzer and an output of the square rooter is
connected to a first input of the divider circuit.
15. The distance measuring instrument according to claim 1 wherein
the variable gain amplifier comprises a digital variable gain
amplifier.
16. The distance measuring instrument according to claim 15 wherein
the variable gain amplifier further comprises a maximum encoder and
a look-up-table, wherein an output of the maximum encoder is
connected to an input of the look-up-table and an output of the
look-up-table is connected to a gain setting input of the digital
variable gain amplifier.
17. The distance measuring instrument according to claim 1 wherein
the variable gain amplifier comprises a plurality of comparators,
latches and fixed gain amplifiers.
18. The distance measuring instrument according to claim 1 further
comprising a second signal analyzer having a first signal input
connected to an output of the variable gain amplifier, wherein the
second signal analyzer is configured to determine occurrence times
of a signal feature of signals supplied to its first input.
19. The distance measuring instrument according to claim 18 wherein
the second signal analyzer is configured to determine the
occurrence time as a time when the signal supplied to the first
input of the second signal analyzer exceeds a predetermined
level.
20. The distance measuring instrument according to claim 19 wherein
the predetermined level is a fixed level.
21. The distance measuring instrument according to claim 19 wherein
the predetermined level is a variable level depending on an output
of the first signal analyzer.
22. The distance measuring instrument according to claim 21 wherein
the second signal analyzer comprises a second signal input
connected to the output of the first signal analyzer.
23. The distance measuring instrument according to claim 18 wherein
the second signal analyzer comprises a first analog/digital
converter configured to generate a series of digital values
representing subsequent readings of a signal supplied to the first
signal input of the second signal analyzer.
24. The distance measuring instrument according to claim 23 wherein
the second signal analyzer is configured to process the generated
series of digital values based upon an output of the first signal
analyzer.
25. The distance measuring instrument according to claim 18 wherein
the second signal analyzer comprises a second analog/digital
converter having an input connected to the output of the first
signal analyzer.
26. The distance measuring instrument according to claim 18 further
comprising a trigger circuit having an output connected to the
light source, wherein the trigger circuit and the light source are
configured to operate the light source such that it emits
subsequent pulses of measuring light.
27. The distance measuring instrument according to claim 26 wherein
the second signal analyzer is configured to determine the
occurrence times of the signal feature relative to times depending
on emission times of the pulses of measuring light.
28. The distance measuring instrument according to claim 27 wherein
the optics is configured to direct a portion of the measuring light
emitted from the light source directly to the detector, without
directing this portion to the object.
29. The distance measuring instrument according to claim 28 wherein
the second signal analyzer is configured to determine times of
corresponding signal features of subsequent pairs of signal pulses
received at its first input.
30. The distance measuring instrument according to claim 1 wherein
the at least one light source comprises: at least one light guiding
fiber doped with a rare earth element, a pump laser connected to
the at least one light guiding fiber, and a signal laser connected
to the light guiding fiber, wherein the light guiding fiber is
configured to amplify and emit light received from the signal laser
as the measuring light.
31. The distance measuring instrument according to claim 30 wherein
the rare earth element comprises at least one of Ytterbium and
Erbium.
32. The distance measuring instrument according to claim 30 wherein
the at least one light guiding fiber is a double clad fiber having
a single mode fiber core.
33. A distance measuring method comprising: emitting a pulse of
measuring light towards an object; receiving a pulse measuring
light from the object and generating a pulse signal corresponding
to the pulse of measuring light received from the object; delaying
a first portion of the generated pulse signal for a predetermined
time; generating an intensity signal indicative of an intensity of
the generated pulse signal, while delaying the first portion of the
generated pulse signal; amplifying the delayed first portion of the
generated pulse signal using a gain dependent on the generated
intensity signal; and determining a value representing a distance
based on the amplified delayed first portion of the generated pulse
signal.
34. The distance measuring method according to claim 33 wherein the
generating of the intensity signal includes determining a maximum
value of the second portion of the generated pulse signal.
35. The distance measuring method according to claim 33 wherein the
amplifying of the delayed first portion of the generated pulse
signal comprises dividing a signal corresponding to the delayed
first portion by the intensity signal.
36. The distance measuring method according to claim 33 wherein the
determining of the value representing the distance comprises
identifying an occurrence time of a signal feature of the amplified
first portion of the generated pulse signal.
37. The distance measuring method according to claim 33 wherein the
identifying the occurrence time of the signal feature of the
amplified first portion of the generated pulse signal is performed
relative to a time which depends on an emission time of the pulse
of measuring light emitted towards the object.
38. The distance measuring method according to claim 33 further
comprising: generating a light pulse, wherein a first portion of
the generated light pulse forms the pulse of measuring light
emitted towards the object; and receiving a second portion of the
generated light pulse without directing it to the object and
generating a pulse signal corresponding to the received second
portion of light not directed to the object.
39. The distance measuring method according to claim 38 wherein: a
first pulse signal is generated which corresponds to the received
second portion of light not directed to the object; a second pulse
signal is generated which corresponds to the pulse of measuring
light received from the object; and the value representing the
distance is determined based on a temporal distance between the
first and second pulse signals.
Description
[0001] This application claims priority to and is a continuation of
International Patent Application No. PCT/EP2007/008487, filed on
Sep. 28, 2007, the disclosure of which is hereby incorporated by
reference in its entirety for all purposes.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a distance measuring
instrument and a distance measuring method.
[0003] In particular, the invention relates to a distance measuring
instrument and method where modulated measuring light is emitted
towards an object and wherein measuring light received back from
the object is detected and analyzed. A value representing a
distance from the object is determined based on such analysis.
[0004] A conventional distance measuring instrument comprises a
laser generating pulses of measuring light, and optics to direct
the pulses of measuring light towards an object. Pulses of
measuring light received back from the object are supplied to a
light sensor to generate electrical signals corresponding to the
light pulses, and the electrical pulse signals are amplified and
analyzed. The analysis includes determination of occurrence times
between subsequent pulses to determine the distance from the object
based on the determined occurrence times.
[0005] It has been found that the conventional distance measuring
instruments and methods could be improved with respect to at least
one of measurement accuracy, measurement speed and distance
measuring range.
SUMMARY OF THE INVENTION
[0006] The present invention has been accomplished taking the above
problems into consideration.
[0007] Embodiments of the present invention provide a distance
measuring instrument and distance measuring methods having advanced
performance, in particular with respect to accuracy or speed.
[0008] According to an embodiment of the invention, the distance
measuring instrument comprises a variable gain amplifier for
amplifying a detected signal, wherein a higher gain is applied when
the detected signal has a low intensity and wherein a relatively
lower gain is applied when the detected signal has a relatively
higher intensity.
[0009] According to a further embodiment of the present invention,
the distance measuring instrument comprises a first analyzer for
analyzing the detected signal such that the gain of the variable
gain amplifier can be set based on a result of this analysis.
[0010] According to a further embodiment, the distance measuring
instrument comprises a signal delay module for delaying a first
portion of a detected signal, wherein a first analysis of a second
portion of the detected signal is performed while the first portion
is delayed. According to an embodiment herein, it is then possible
to derive a gain value from the analyzed second portion of the
detected signal, and to supply the derived gain value to the
variable gain amplifier such that the gain of the variable gain
amplifier is set when the delayed first portion of the detected
signal arrives for amplification. The variable gain amplifier will
then amplify the detected signal according to the currently
supplied gain value.
[0011] In particular embodiments, the gain value is determined such
that the amplified signal outputted from the variable gain
amplifier has a substantially constant intensity which is
relatively independent of the intensity of the detected signal. The
amplified signal can then be subject to further analysis, wherein
this analysis is relatively independent of the intensity of the
original detected signal. This can be of a particular advantage in
practice since measuring light received back from the object and
the corresponding detected signals may vary by many orders of
magnitude, depending on the distance of the object from the
measuring instrument and on an albedo of the object.
[0012] According to an exemplary embodiment of the invention, a
distance measuring instrument comprises at least one light source;
at least one light detector; optics to direct measuring light
emitted from the at least one light source towards an object and to
direct measuring light received back from the object to the at
least one detector; a signal delay module; a first signal analyzer;
and a variable gain amplifier; wherein: an output of the at least
one light sensor is connected to an input of the signal delay
module; the output of the at least one light sensor is connected to
a signal input of the first signal analyzer; an output of the
signal delay module is connected to a signal input of the variable
gain amplifier; and an output of the first signal analyzer is
connected to a gain setting input of the variable gain
amplifier.
[0013] As used in the context of this application, the term
connected is not limited to mean directly connected but shall also
encompass functional connections with intermediate components. For
example, if an output of a first component is connected to an input
of a second component this comprises a direct connection wherein an
electrical conductor directly supplies an outputted signal from the
first component substantially unchanged to the input of the second
component, and this also comprise that the connection is via one or
more additional components, such as an intermediate amplifier or
filter which modifies the signal outputted from the first component
before it is inputted to the second component. Still, the
connection is a functional connection in that, if the signal
outputted from the first component undergoes gradual or prompt
changes, a corresponding and maybe modified change will be applied
to the input of the second component.
[0014] According to exemplary embodiments of the invention, the
signal delay module delays an inputted signal by a predetermined
signal delay time before it is outputted. The signal delay time can
be greater than or equal to one of a processing time associated
with the first signal analyzer, a settling time associated with the
variable gain amplifier, and a sum of the processing time of the
first signal analyzer and the settling time of the variable gain
amplifier.
[0015] The processing time associated with the first signal
analyzer is defined in the context of the present invention as the
time elapsed from the application of an ideal instantaneous step
signal to the input of the first signal analyzer to a time at which
the output of the first signal analyzer has entered and remained
within a value range between 0.5 to 1.5 times the final value
established at the output of the first signal analyzer.
[0016] Similarly, the settling time associated with the variable
gain amplifier is defined in the context of the present invention
as the time elapsed from supplying the settled output from the
first signal analyzer to the variable gain amplifier and a time
when the variable gain amplifier has adjusted its amplification to
its final value with an accuracy within 0.5 to 1.5 times the final
value of the adjusted amplification.
[0017] According to exemplary embodiments, the signal delay time is
greater than one of 0.5 ns, 1.0 ns, 3 ns, 5 ns and 7 ns.
[0018] According to exemplary embodiments, the first signal
analyzer is configured to provide an output signal at its output
which is indicative of an intensity of an input signal supplied to
its signal input. For example, the output signal can be indicative
of a peak value of the input signal, wherein a maximum amplitude of
the input signal may represent the peak value. However, other
values, such as an integrated energy and other suitable values, can
be determined by the first signal analyzer to be indicative of the
intensity or other characteristics of the input signal.
[0019] According to an exemplary embodiment, the variable gain
amplifier is an analog amplifier. In an exemplary embodiment
herein, the variable gain amplifier comprises a divider
circuit.
[0020] According to other exemplary embodiments, the variable gain
amplifier is a digital amplifier. According to exemplary
embodiments herein, the variable gain amplifier comprises plural
fixed gain amplifiers.
[0021] According to exemplary embodiments, the distance measuring
instrument comprises a second signal analyzer having a first signal
input connected to an output of the variable gain amplifier. Thus,
the second signal analyzer receives the amplified detected signal
for further analysis. In particular, the amplified signals may have
a substantially normalized intensity such that the analysis
performed by the second signal analyzer may be substantially
independent of the intensity of the received signal.
[0022] According to exemplary embodiments, the second signal
analyzer is configured to determine occurrence times of a
predetermined signal feature of signals supplied to its input. For
example, the signal feature may be defined as an occurrence where
the signal level exceeds a predetermined level. According to an
exemplary embodiment, the predetermined level is a fixed level.
According to another exemplary embodiment, the predetermined level
is a variable level which depends on some other input. For example,
the variable level may depend on an output of the first signal
analyzer which is indicative of the intensity of the detected
signal.
[0023] According to an exemplary embodiment, the second signal
analyzer comprises a second signal input connected to the output of
the first signal analyzer.
[0024] According to a further embodiment, the second signal
analyzer is configured to determine the occurrence times of the
signal feature relative to emission times of pulses of measuring
light directed to the object.
[0025] According to an exemplary embodiment herein, a portion of
the measuring light emitted from the light source is directly
incident on the light detector, without being directed to and
received back from the object. This portion of measuring light
generates a first detected pulse signal which is amplified
according to its intensity and analyzed by the second signal
analyzer to identify a first occurrence time. Subsequently, the
pulse of measuring light received back from the object generates a
second detected signal which is amplified according to its
intensity and similarly analyzed by the second signal analyzer to
determine a second occurrence time. It is then possible to
determine a value based on a difference between the first and
second occurrence times, wherein this value represents a distance
of the object from the measuring instrument.
[0026] According to exemplary embodiments of the invention, the at
least one light source may include a high power pulsed diode laser
and a pulsed microchip laser.
[0027] According to a further embodiment of the invention, the at
least one light source of the distance measuring instrument
comprises a signal laser and a light amplifier including at least
one fiber doped with a rare earth element such as erbium and
ytterbium. The inventors have found that the doped fiber laser has
advantages over Q-switched microchip lasers used as light sources
in conventional distance measuring instruments. For example, the
Q-switched microchip laser does not allow a precise definition of
emission times of light pulses, whereas the doped fiber laser
allows for an accurate timing of emitted light pulses. For example,
it is possible to achieve a definition of emission times of light
pulses from the measuring instrument of about 20 ps or 10 ps, for
example, when a doped fiber laser is used.
[0028] According to further embodiments of the present invention, a
distance measuring method is provided which comprises: emitting a
pulse of measuring light towards an object; receiving a pulse
measuring light from the object and generating a pulse signal
corresponding to the pulse of measuring light received from the
object; delaying a first portion of the generated pulse signal for
a predetermined time; generating an intensity signal indicative of
an intensity of the generated pulse signal, while delaying the
first portion of the generated pulse signal; amplifying the delayed
first portion of the generated pulse signal using a gain dependent
on the generated intensity signal; determining a value representing
a distance based on the amplified delayed first portion of the
generated pulse signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The foregoing as well as other advantageous features of the
invention will be more apparent from the following detailed
description of exemplary embodiments of the invention with
reference to the accompanying drawings. It is noted that not all
possible embodiments of the present invention necessarily exhibit
each and every, or any, of the advantages identified herein.
[0030] FIG. 1 is a schematic illustration of functional components
of an embodiment of a distance measuring instrument according to
the present invention;
[0031] FIG. 2 and FIG. 3 are schematic illustrations of details of
the distance measuring instrument shown in FIG. 1;
[0032] FIG. 4 illustrates a further embodiment of a first signal
analyzer shown in FIG. 1;
[0033] FIG. 5, FIG. 6, and FIG. 7 are illustrations of further
embodiments of a variable gain amplifier shown in FIG. 1;
[0034] FIG. 8 is an illustration of details of a distance measuring
instrument according to a further embodiment;
[0035] FIG. 9 is an illustration of details of a distance measuring
instrument according to a further embodiment;
[0036] FIG. 10 is a schematic illustration of detected pulses
having different intensities;
[0037] FIG. 11 is an illustration of a further embodiment of the
second signal analyzer shown in FIG. 1;
[0038] FIG. 12 is an illustration of a still further embodiment of
the second signal analyzer shown in FIG. 1; and
[0039] FIG. 13 is an illustration of details of a distance
measuring instrument according to a further embodiment;
[0040] FIG. 14 is an illustration of details of a distance
measuring instrument according to a further embodiment;
[0041] FIG. 15 and FIG. 16 are schematic illustrations of further
embodiments of light sources which can be used in the distance
measuring instrument shown in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0042] In the exemplary embodiments described below, components
that are alike in function and structure are designated as far as
possible by alike reference numerals. Therefore, to understand the
features of the individual components of a specific embodiment, the
descriptions of other embodiments and of the summary of the
invention should be referred to.
[0043] FIG. 1 is a block diagram schematically illustrating an
embodiment of a distance measuring instrument according to the
present invention.
[0044] The distance measuring instrument 1 generates and emits
measuring light towards a remote object 3 where a portion of the
incident measuring light is diffused such that it can be received
by the instrument 1. The measuring light received from the object
is analyzed to determine a distance of the object 3 from the
instrument 1. For this purpose, the instrument 1 comprises a light
source 5 which generates the measuring light, optics 7 to direct
the measuring light emitted from the light source 5 towards the
object 3 and to receive measuring light back from the object. The
instrument 1 further comprises a light detector 9 for detecting the
measuring light received back from the object 3 and to generate
electrical signals corresponding to intensities of the light
received back from the detector.
[0045] The term measuring light as used in the present application
should generally encompass electromagnetic radiation of any
wavelength or wavelength range suitable for distance measurement,
such as microwave radiation, visible light and invisible light. In
the illustrated embodiment, the light source 5 is a laser, such as
a microchip laser, a doped fiber laser or other suitable laser.
Light 9 emitted from the laser enters a prism 11 which includes a
partially reflective surface 13 and a mirror surface 14. A small
monitoring portion 10 of the emitted light 9 is reflected from
partially reflective surface 13 to be incident on a mirror surface
14 which directs that portion 10 onto the detector 9.
[0046] The instrument 1 further comprises an analyzer and control
system 21 for analyzing the detected measuring light, determining
measuring results and controlling the whole instrument.
[0047] The monitoring portion 10 of the emitted light 9 is directed
to the detector to allow the analyzing and control system 21 to
monitor the emitted measuring light. For example, the analyzing and
control system 21 may determine occurrence times of particular
features of that portion 10 which are relevant for the distance
measurement. For example, a start time of a distance measurement
can be determined based on the detection and analysis of the
monitoring portion 10 of the light 9 emitted from the light source
5. A larger portion 17 of the light 9 emitted from the source 5
traverses the partially reflective surface 13 and is reflected from
a mirror surface 15, and further reflected from a mirror 18 such
that the measuring light reflected from mirror 18 is directed along
an optical axis 21 of a lens 23. The lens 23 is schematically
represented in FIG. 1 as a single lens element. In practice,
however, the lens 23 may include plural lens elements to form an
objective lens suitable to direct the measuring light along the
optical axis 21 towards the object 3. For this purpose, the lens 23
may have functions for focusing the measuring light onto objects 3
at variable distances. A cross section of lens 23 is larger then
necessary to emit the measuring light towards the object, wherein
the exceeding portion of the cross section is used for receiving
measuring light 25 reflected back from the object 23 and for
directing this measuring light 25 onto the detector 9.
[0048] In the exemplary embodiment shown with reference to FIG. 1,
a portion of the light pulse directed to the object is branched off
by reflective surfaces 13 and 14 to be incident on detector 9 which
is the same detector which also receives the light pulse reflected
back from the object. Thus, both the start time and the stop time
of the distance measurement are derived from light pulses incident
on the same detector 9. In other embodiments, the start time of the
distance measurement is determined by other principles. For
example, the instrument may comprise an additional light detector,
such as a PIN diode to receive a portion of the light pulse emitted
towards the object. The start time of the distance measurement can
then be generated based on output signals of such additional
detector.
[0049] Further, it is possible to determine the start time of the
distance measurement directly from an occurrence time of a trigger
signal for emitting light pulses from the light source. To take
into account possible time delays and offsets in determination of
the start time, it is possible to calibrate the instrument relative
to an object disposed at a known distance from the instrument, for
example.
[0050] The detector 9 generally includes a sensor portion receiving
the incident light and a circuit portion to generate electrical
signals corresponding to intensities of the incident light. The
detector 9 may include an amplifier for adjusting a signal level
and impedance of the generated electrical signal such that it is
suitable for subsequent analysis by the analyzer and control system
21.
[0051] The analyzing and control system 21 comprises an analyzer 31
for analyzing shapes or characteristics of the electrical signals
provided at the output 29 of detector 9. However, intensities of
the signals outputted from the detector 9 may vary by plural orders
of magnitude depending on a distance of the object 3 from the
instrument 1 and on an albedo of the object 3. The signals provided
by the detector 9 have a very high dynamic range, accordingly,
whereas the analyzer 31 has a limited dynamic range determined by a
configuration of the analyzer 31. Therefore, the analyzer and
control system 21 comprises a variable gain amplifier 33 configured
to amplify signals provided by the detector 9 with a suitable gain
such that the amplified signal has intensities within a reduced
dynamic range suitable for analysis by analyzer 31. An output 35 of
the variable gain amplifier 33 is connected to a first signal input
36 of analyzer 31.
[0052] The term variable gain amplifier as used in the present
invention should not be limited to amplifiers having always gains
larger than 1 such that a signal level outputted from the output 35
of the variable gain amplifier is always greater than a signal
level of a signal supplied to a signal input 37 of the variable
gain amplifier 33. The gain of the variable gain amplifier may be
set to values less than 1, accordingly.
[0053] The analyzer and control system 21 comprises a signal
analyzer 41 for determining the gain used by the variable gain
amplifier 33 wherein a signal representing the gain is outputted
from an output 42 of the signal analyzer 41 and supplied to a gain
setting input 43 of the variable gain amplifier 33. A signal input
45 of the signal analyzer 41 is connected to the output 29 of the
detector 9 such that the signal analyzer 41 receives a portion of
the detection signal generated by the light detector 9. The signal
analyzer 41 is configured to determine the gain based on a
characteristic of the output signal, such as an intensity of the
output signal of the light detector 9. For this purpose, the signal
analyzer 41 has to process the inputted signal. Such processing
will take a certain amount of processing time depending on the
configuration of the signal analyzer 41. The signal representing
the gain to be applied by the variable gain amplifier 33 will be
available at the output 42 of signal analyzer 41 at a time which is
later than an arrival time of the signal at the signal input 45 of
signal analyzer 41. Further, when the signal representing the gain
is available at the output 42 of signal analyzer 41 and supplied to
the gain setting input 43 of the variable gain amplifier 33, the
variable gain amplifier 33 will need a certain amount of time
depending on the configuration of the variable gain amplifier until
the gain of the amplifier is precisely adjusted according to the
inputted gain value. This amount of time is referred to as the
settling time of the variable gain amplifier 33. It follows that
the variable gain amplifier 33 is ready for amplification of a
given detection signal at a point in time which is later than a
time at which the signal to be amplified with the variable gain is
available at the output 29 of the detector 9.
[0054] Therefore, in the illustrated example, the signal input of
the variable gain amplifier 33 is not directly connected to the
output 29 of the light detector 9, and a signal delay module 51 is
arranged in a signal path between the light detector 9 and the
variable gain amplifier 33. In more detail, the delay module 51 has
a signal input 52 which is connected to the output 29 of the light
detector 9, and a signal output 53 of the delay module 51 is
connected to the signal input 37 of the variable gain amplifier 33.
The delay module is configured to receive a given signal at its
input 52 and to make a substantially same or similar signal
available at its output 53 wherein the outputted signal is delayed
relative to the inputted signal by a predetermined delay time. The
delay module 51 may comprise, for example, a delay line, a surface
acoustic wave device or other device suitable for delaying an
inputted signal by a predetermined amount of time. In the
illustrated example, the delay time of the delay module is selected
such that it is greater than a sum of the processing time of the
signal analyzer 41 and the settling time of the variable gain
amplifier 33. By such arrangement it is possible to complete the
setting of the gain of the variable gain amplifier 33 until the
signal to be amplified with the set gain arrives at the signal
input 37 of the variable gain amplifier 33. For example, if the
signal analyzer 41 is configured such that it has a processing time
of 3 ns and if the variable gain amplifier 33 is configured such
that it has a settling time of 2 ns, the delay module is designed
such that it has a delay time of 5 ns or 6 ns or more.
[0055] As mentioned above, the signal analyzer 41 is configured to
determine an intensity of a signal supplied to its input 45. In the
illustrated embodiment, the signal analyzer 41 is configured such
that it detects a peak amplitude of the signal supplied to its
input 45 as the signal intensity. Further, the signal analyzer 41
has a reset input 55 to which a predefined signal can be applied
for resetting the signal analyzer such that it starts to analyze a
next signal supplied to its signal input 45. For example, if the
signal to be analyzed is a pulse shape, the signal analyzer 41 can
determine the intensity of the pulse or, in the given example,
determine the peak value of the pulse, and provide a corresponding
signal at its output 42. A level of that signal representing the
gain to be used by the variable gain amplifier 33 will be
maintained constant until the signal analyzer 41 is reset by
supplying the reset signal to its reset input 55. Thereafter, the
signal analyzer 41 is prepared to analyze the intensity of a next
pulse signal supplied to its signal input 45.
[0056] A configuration of the signal analyzer 41 and the variable
gain amplifier 33 is shown in more detail in FIG. 2.
[0057] FIG. 2 is a schematic illustration of components of a
portion of the analyzer and control system 21. In the illustrated
example, the variable gain amplifier comprises an x/y divider 61,
wherein the x input of the x/y divider 61 is connected to the
signal input 37 of the variable gain amplifier and wherein the y
input of the x/y divider 61 is connected to the gain setting input
43 of the variable gain amplifier 33. As shown in FIG. 2, it is
possible to provide a fixed gain amplifier 63 in the signal path
between the output 53 of the delay module 51 and the x input of the
x/y divider. A signal output of the x/y divider is connected to or
provides the output 35 of the variable gain amplifier.
[0058] The signal analyzer 41 comprises a high speed peak detector
and hold module 67 having a signal input S providing the signal
input 45 of the signal analyzer 41, a reset input R providing the
reset input 55 of the signal analyzer 41, and an output O which is
connected to a first signal input S.sub.1 of an analog MAX module
69 which outputs the maximum of the two signals supplied to its
inputs S.sub.1 and S.sub.2. The input S.sub.2 is used to supply a
signal S.sub.f to the signal analyzer 41, wherein the signal
S.sub.f represents a maximum gain to be applied to the variable
gain amplifier 33.
[0059] An output O of the MAX module 69 is connected to a first
signal input S.sub.1 of a MUX analog module 71 which further
includes a second signal input S.sub.2, a signal output O and a
choice input C. The MUX module is configured to output one of the
two signals supplied to its inputs S.sub.1 and S.sub.2 depending on
a choice signal supplied to its choice input C.
[0060] In a first mode, where a choice signal selects input S.sub.2
as the output of the MUX module 71, a fixed gain corresponding to a
level V.sub.g can be supplied to input S.sub.2 of the MUX module 71
to set the gain of the variable gain amplifier 33 to a value
represented by level V.sub.g. The gain of the x/y divider 61 is
then set to 1/V.sub.g, which is independent on the intensity of the
signal S supplied to the input 45 of the signal analyzer 41. This
mode effectively disables the signal analyzer 41 and can be used
when the adaptive amplification of the inputted signals S depending
on their intensities is not desired.
[0061] In a second mode, where the choice signal is selected such
that input S.sub.1 of MUX module 71 is selected for output, the
intensity analyzing operation of the signal analyzer 41 is enabled
wherein the gain value provided at output 42 of signal analyzer 41
depends on the intensity of the signal S supplied to the input 45.
However, a maximum gain can be set by supplying a signal level
S.sub.f representing the maximum gain to the S.sub.2 input of the
MAX module 69.
[0062] FIG. 3 is a more detailed illustration of further components
of the analyzer and control module 21. As shown in FIG. 3, the
signal analyzer 31 comprises a fast analog digital converter 75
having an analog input 76 which receives the amplified signal
S/S.sub.0 from the output 35 of the variable gain amplifier 33,
where S.sub.0 is the output 42 of the analyzer 41, for example the
maximum amplitude of the signal S. The analog digital converter 75
is driven by a clock 81 such that the signal level supplied to the
input 76 is sampled according to a rate determined by the clock 81,
and digital values representing the signal level supplied to the
input 76 are made available at an output 77 of the analog digital
converter according to the rate determined by the clock 81. These
digital values are then written into a memory 83 at addresses
selected by an address generator 85. Also the address generator 85
is driven by the clock 81 such that the address selected by the
address generator 85 is advanced according to the rate determined
by the clock 81. Thus, subsequent digital readings of the analog
input signal are stored in subsequent memory locations. The memory
83 is accessible from a controller 91 which can be any suitable
computing device or network of devices such as personal computers
or other hardware.
[0063] The controller 91 can be connected to user interface
devices, such as a display 92 and a keyboard 93, or other suitable
user interfaces such as touch screens, for example.
[0064] The controller 91 accessing the memory 83 can perform an
analysis of the recorded digital values. For example, the
controller may determine features of the digitized signal, such as
occurrences of signal values exceeding a threshold or a center of
gravity of a digitized pulse signal.
[0065] The controller 91 may also calculate a time when the
determined signal feature occurred. Further, if there are two
subsequent digitized pulses stored in the memory, the controller
can determine the centers of gravity of both signals in terms of
memory addresses and then calculate a temporal distance between the
occurrence of two pulses based on a rate of the clock 81 advancing
the address generator 85. Assume that a first one of such two
digitized pulses stored in memory corresponds to the monitoring
portion 10 of a light pulse 9 emitted by the light source 5 and
incident directly onto the light detector 9 whereas the second of
such digitized light pulses stored in memory corresponds to the
portion 17 of the emitted light pulse directed to and received back
from the object 3, then the temporal distance between the two
analyzed signals represents the distance of the object 3 from the
measuring instrument 1, wherein the distance of the object can be
calculated as the temporal distance times the speed of light
divided by two.
[0066] The distance measuring instrument as shown in FIG. 1 further
comprises an actuator 95 driven by the controller 91 for changing
an orientation of the optical axis 21 of optics 7. For example, the
optics 7, light source 5 and detector 9 can be arranged as a module
which is rotatable relative to a stand placed on the ground about a
horizontal axis and a vertical axis. The controller 91 can then
drive the actuator 95 such that the object 3 is scanned with
measuring light wherein the distance of subsequent scan points of
the object 3 from the measuring instrument 1 is determined as
illustrated above. The resulting data, also refer to as a point
cloud, can be stored by the controller 91 for further analysis in a
memory, such as a hard disc 97 shown in FIG. 1.
[0067] Further exemplary embodiments of the present invention will
be described below.
[0068] FIG. 4 is a schematic illustration of a portion of an
analyzer and control system 21a of a distance measuring instrument
1a which can be of a similar structure as that illustrated with
reference to FIG. 1 above. A signal analyzer 41a shown in FIG. 4
provides the combined functions of a high speed peak detector and
hold module and MAX module as represented by a functional box 41'
shown in broken lines in FIG. 2. The signal analyzer 41a comprises
a gain 1 buffer, for example an operational amplifier 101 having a
non-inverted input which is supplied with the input signal S via an
ideal diode 103, and an inverted input which is supplied with a
feedback from its output. A hold capacitor 105 is connected to the
non-inverting input of the operational amplifier 101 and is charged
with a voltage S.sub.f representing the maximum gain upon operation
of a reset switch 107.
[0069] FIG. 5 shows an exemplary embodiment of a variable gain
amplifier 33b of an analyzer and control system 21b of a distance
measuring instrument 1b which can be similar in structure to that
shown in FIG. 1. The variable gain amplifier 33b comprises an xy
multiplier 111 having a X input which is supplied with the signal S
to be amplified via a constant gain amplifier 63b, wherein it is
also possible to omit the amplifier 63b and directly supply the
signal S to be amplified to the X input of the xy multiplier. An
operational amplifier 113 receives the signal S.sub.0 representing
the reciprocal gain at its inverting input via a resistor, and a
non-inverting input of operational amplifier 113 is connected to
ground. An output of the operational amplifier 113 provides the
output O of the variable gain amplifier 33b at an output 35b,
wherein the output of the operational amplifier 131 is also
connected to the Y input of the xy multiplier 111. An output of the
xy multiplier is supplied as a feedback via a resistor R to the
inverting input of operational amplifier 113.
[0070] FIG. 6 is a schematic illustration of a further embodiment
of a variable gain amplifier 33c which may have an improved
bandwidth, in particular for low levels of input signal S, as
compared to the embodiment shown in FIG. 5. The variable gain
amplifier 33c comprises an xy multiplier 121 having an X input
supplied with the signal S to be amplified via a fixed gain
amplifier 63c, and an Y input connected to an output of a xy
divider 123. The xy divider has an X input supplied with a constant
signal (represented as "1" in FIG. 6), and an Y input supplied with
the reciprocal gain S.sub.0.
[0071] FIG. 14 is a schematic illustration of a further embodiment
of a variable gain amplifier 331 which is a variation of the
variable gain amplifier shown in FIG. 6. In the variable gain
amplifier 331 shown in FIG. 14, an Y input of a multiplier 1211 is
connected to an output of a multiplier 261 which receives its x and
y inputs from outputs of differential amplifiers 263 and 265. Such
arrangement allows to shape the divider function by constants a, b
and c supplied to the differential amplifiers 263, 265 and the
multiplier 261. It is further possible to provide further
additional combinations of multipliers and differential amplifiers
to increase the number of constants a, b, c, . . . for shaping the
divider function.
[0072] FIG. 7 shows a further embodiment of a variable gain
amplifier 33d which could be used in the distance measuring
instrument shown in FIG. 1. The variable gain amplifier 33d
comprises an xy multiplier 127 having an X input supplied with the
signal S to be amplified, and an output which is connected to an X
input of a further xy multiplier 129. An output of the xy
multiplier 129 provides the output of the variable gain amplifier
33d. The reciprocal gain S.sub.0 is supplied to the input of a
square rooter 131, and an output of the square rooter 131 is
connected to an Y input of a xy divider 133. A constant signal
(represented by "1" in FIG. 7) is supplied to an X input of xy
divider 133. An output of the xy divider 133 is connected to Y
inputs of both xy multipliers 127 and 129.
[0073] FIG. 8 illustrates a portion of a further embodiment of an
analyzer and control system 21e which could be used in a distance
measuring instrument according to an embodiment of the invention.
In the embodiment shown in FIG. 8, a signal analyzer 41e and a
variable gain amplifier 33e are implemented using digital
electronics. The signal analyzer 41e comprises an analog digital
converter 141 supplied with the signal S generated by a light
detector. The signal is digitized by the analog digital converter
141 and supplied as a digital signal to a maximum encoder 143 which
provides a maximum value of the received digital values at an
output 42e of the signal analyzer 41e.
[0074] The variable gain amplifier 33e comprises a digital variable
gain amplifier 151 having a signal input which is supplied with the
signal to be amplified from a delay module 51e. The digital
representation of the peak signal provided at the output 42e of the
signal analyzer 41e can be directly supplied to a digital gain
input of digital variable gain amplifier 151. In the embodiment
shown in FIG. 8, a look-up table 153 is provided to receive the
representation of the peak value and to translate this peak value
to a gain which is supplied to the digital gain input of the
digital variable gain amplifier 151. The look-up table is prepared
in advance to take possible non-linear effects of the digital
variable gain amplifier 151 into account or to achieve a desired
further variation of the gain to be applied for amplification of
the signal S based on the peak value detected by signal analyzer
41e.
[0075] FIG. 9 is a schematic illustration of a portion of an
analyzer and control system 21f according to a still further
embodiment of the present invention. A signal analyzer 41f of
system 21f comprises an array of plural high speed comparators and
latches 161. For example, a number of the comparators and latches
may be six. Each of the comparators and latches is supplied with
the signal S to be analyzed, and the signal analyzer 41f further
comprises an array of plural maximum encoders 163, wherein each
maximum encoder is connected to a corresponding latch of the array
of comparators and latches 161. The outputs of the plural maximum
encoders 163 form a digital representation of the analyzed signal
S. These outputs of the maximum encoder 163 also drive a
corresponding number of high speed turn on/off switched amplifiers
33f such that an output 35f thereof provides the delayed and
amplified signal S wherein the gain applied for amplification is
dependent on a peak level of the signal S.
[0076] Reference is now made to FIG. 1, wherein the signal analyzer
31 is generally configured to determine occurrence times of signal
features of the signal S generated by the light source 9.
[0077] FIG. 10 is a schematic illustration of possible temporal
pulse shapes of signal S. FIG. 10a shows a pulse 171 of a
relatively small peak value, whereas FIG. 10b shows a pulse 172 of
a relatively higher peak value. An occurrence time of the signal
peaks is indicated by tp. Since it is not easily possible to
determine the occurrence times t.sub.p of the peak values, the
signal analyzer 31 can be configured to determine occurrence times
t.sub.f of features different from the occurrence times t.sub.p of
the peak values. For example, the occurrence times t.sub.f can be
defined as those times when the signal exceeds a predetermined
constant threshold Lc. It is apparent that the times t.sub.f occur
earlier than the peak times t.sub.p wherein a difference
t.sub.p-t.sub.f depends on the intensity of the signal. It is
desirable to determine feature times t.sub.f which are indicative
of the occurrence times of the peak values t.sub.p independently of
the intensity of the signals.
[0078] FIG. 11 illustrates an embodiment of a signal analyzer 31g
which could be used in the distance measuring instrument
illustrated in FIG. 1. The signal analyzer 31g comprises a very
fast comparator 181 having a first input receiving the signal to be
analyzed from a delay module (not shown in FIG. 11), and having a
second input connected to an output of a multiplier 183. Multiplier
183 has an input connected to a second signal input 185 of the
signal analyzer 31g and which is connected to an output of signal
analyzer 41 and representing the gain to be applied by the variable
gain amplifier 33. The multiplier is configured to multiply the
signal supplied to its input by a fixed factor, such as 0.5 in the
illustrated example. An output S.sub.d of the comparator 181 may
then provide a step-shaped signal which changes value when the
signal supplied at input 36g exceeds the signal supplied at input
85 and multiplied by the fixed factor. The occurrence time of
change of value of the signal S.sub.d can then be used as the
feature time t.sub.f of the analyzed signal, and such feature time
t.sub.f is a better representation of the occurrence time t.sub.p
of the peak value of the signal at varying signal intensities as
compared to using a constant threshold as illustrated in FIG. 10
above.
[0079] Reference is now made to FIG. 3: The signal analyzer shown
in FIG. 3 further comprises an analog digital converter 187 to
translate the analog value provided by signal analyzer 41 and which
represents the gain applied to the variable gain amplifier into a
digital value. This digital value is accessible by the controller
91 and can be taken into account when the occurrence times of the
signals are determined by the controller 91.
[0080] FIG. 12 illustrates a further embodiment of a signal
analyzer 31h which has a configuration similar to that shown in
FIG. 11 in that multipliers 183a are connected to inputs of vary
fast comparators 181a. The other inputs of the vary fast
comparators 181a are all supplied with the amplified signal to be
analyzed. However, an array of multipliers 183a and comparators
181h is provided, wherein the multipliers 183a are configured to
multiply their input signals with different fixed vectors x.sub.1,
. . . , x.sub.i, . . . , x.sub.n. Outputs S.sub.d1, . . . ,
S.sub.di, . . . , S.sub.dn represent occurrence times of different
features of the analyzed signals, wherein the different occurrence
times are those times where the signal exceeds different signal
levels determined by the multiplication factors x.sub.i of the
multipliers 183h. This allows to analyze the occurrence times at
different levels of the signal, wherein the signal noise will be
different at different signal levels. The possibility of analyzing
the signal at different levels may then improve the total
accuracy.
[0081] FIG. 13 illustrates a further embodiment of components of an
analyzing and control system 21k which can be used in embodiments
of the distance measuring instrument.
[0082] The analyzing and control system 21k comprises a signal
analyzer 41k for determining the gain to be used for amplifying a
signal S as supplied to both the signal analyzer 41k and a delay
module 51k. The arrangement of components shown in FIG. 13 is
similar to that shown in FIG. 2, wherein a variable gain amplifier
33k is embodied as a multiplier 111k. However, in the arrangement
shown in FIG. 13, baluns 251 are connected to an output 42k of the
signal analyzer 41k and an output 53k of the delay module 51k,
respectively, for supplying the respective signals to the
multiplier 111k via two symmetric lines. Further, a level shifter
253 is provided in the symmetric line between the output 42k of the
signal analyzer 41k and an input of the multiplier 111k. A further
balun 251 is connected to the symmetric line output of the
multiplier 111k such that an output 35k of the amplified signal is
again on an asymmetric line.
[0083] FIG. 15 shows a possible embodiment of a light source 5i
which can be used in the distance measuring instrument shown in
FIG. 1. The light source 5i comprises a signal laser 201 driven by
a controller 91i to generate light pulses at a repetition rate
determined by controller 91i and which may range, for example, from
1 kHz to 1000 kHz. The signal laser 201 may have an output power in
a range from 1 to 20 mW, for example. It is, however, also possible
to use light sources of a substantially higher output power having
peak powers of about 5 W, for example. The signal laser may include
a temperature stabilization or not.
[0084] The laser light generated by the signal laser is amplified
by a two-stage amplifier 203 having a first stage 205 and a second
stage 207, wherein each stage comprises a single mode rare earth
doped fiber 209 and a wavelength division multiplexer 211. The rare
earth element used for doping the fiber is erbium in the present
example.
[0085] Both the light to be amplified and the pump light are
supplied to the doped fibers 205 via the wavelength division
multiplexers 211. The pump light is generated by a pump laser 213
and supplied to the wavelength division multiplexers 211 of stages
205 and 207 via a beam splitter 215. To avoid spontaneous emission
of light and amplification thereof in the second stage 207, an
optical filter 217 is provided between the two stages 205 and 207.
The filter 217 may include an optical isolator, a wavelength filter
and a time gating device, such as an acousto optic modulator, an
electro optic modulator and a saturable absorber. In the present
example, the filter 217 is a narrow-band wavelength filter and an
optical isolator.
[0086] In the embodiment illustrated with reference to FIG. 15
above, the light is amplified in a single mode rare earth doped
fiber, wherein the pump light is supplied into the fiber via a
wavelength division multiplexer. It is also possible to use double
clad fibers having a single mode rare earth doped core included in
a clad to which the pump light is supplied. The pump light then
enters the core on the clad.
[0087] While the embodiment of the light source illustrated with
reference to FIG. 15 above includes a two stage amplifier, it is
also possible to use light sources having more than two
amplification stages.
[0088] FIG. 16 schematically illustrates a further embodiment of a
light source 5j which can be used in the instrument illustrated in
FIG. 1. The light source 5j in FIG. 16 comprises a signal laser
201j generating output light which is supplied to a port 1 of a
circulator 221. This light is outputted from a port 2 of the
circulator 221 to be supplied to a rare earth doped fiber 209j. An
amplified signal emitted from the fiber 209j traverses a wavelength
division multiplexer 221j and is reflected from a combined filter
and mirror 223 such that it again traverses the wavelength division
multiplexer 221j to be further amplified in a doped fiber 209j. The
further amplified light enters the circulator 221 at its port 2 and
exits the circulator 221 at its port 3 to form measuring light 9j
which can be emitted towards an object.
[0089] The doped fiber 209 is pumped with light from a pump laser
213j which is coupled into the fiber via the wavelength division
multiplexer 221j.
[0090] While the invention has been described with respect to
certain exemplary embodiments thereof, it is evident that many
alternatives, modifications and variations will be apparent to
those skilled in the art. Accordingly, the exemplary embodiments of
the invention set forth herein are intended to be illustrative and
not limiting in any way. Various changes may be made without
departing from the spirit and scope of the present invention as
defined in the following claims.
* * * * *